1. Field of the Invention
The present invention relates to a signal processor, a control method, and a wireless communication device.
2. Description of the Related Art
In these days, research and development on a MIMO (Multiple Input Multiple Output) communication system described, for example,
in “IEEE802.11n” (prepared by the 802.11 Working Group of the 802 Committee, 2007) is performed widely. The MIMO communication system is a communication system in which a plurality of antennas is provided on each wireless communication device, the wireless communication device receives signals multiplied spatially transmitted from the antennas, through the antennas, and the received signals are separated by using a signal separation technique such as an inverse matrix operation. According to the MIMO communication system, it is possible to improve the transmission speed.
More specifically, the wireless communication device has to include a plurality of DA converters, analog transmission processing units, analog reception processing units, and AD converters respectively, in addition to the antennas, in order to realize the MIMO communication system. Each of the analog transmission processing units frequency-converts a baseband signal of analog format output from the DA converter, for example, into a high frequency signal of 5 GHz band and the antenna transmits the high frequency signal as a wireless signal. Each of the analog reception processing units down-converts the high frequency signal received by the antenna as the wireless signal into the baseband signal of analog format and outputs it to the AD converter.
Such a wireless communication device has to calibrate property errors in the antenna, the DA converter, the analog transmission processing unit, the analog reception processing unit, and the AD converter, or to do calibration there. Hereinafter, the calibration for the analog transmission processing unit, the analog reception processing unit, the DA converter, and the AD converter is referred to as an IQ calibration and the calibration for the antenna is referred to as an antenna calibration.
There is a case where IQ calibration includes a series of flow of returning back a reference signal through a path of the DA converter, the analog transmission processing unit, the analog reception processing unit, and the AD converter in this order and calibrating the property errors in each component mentioned above, according to the returned reference signal. While, there is a case where the antenna calibration includes a series of flow of transmitting a reference signal through the DA converter, the analog transmission processing unit, and the antenna, returning back another reference signal received in another antenna through the path of the analog reception processing unit and the AD converter, and calibrating the property error of the antenna according to the returned reference signal.
Here, the calibration in the wireless communication device has to satisfy, for example, the following three constraints.
(1) A combination of the analog transmission processing unit and the DA converter and a combination of the analog reception processing unit and the AD converter at a time of the antenna calibration are the same as in the ordinary wireless communication.
(2) A combination of the analog transmission processing unit and the DA converter and a combination of the analog reception processing unit and the AD converter at the time of the IQ calibration are the same as in the ordinary wireless communication.
(3) The analog transmission processing unit and the analog reception processing unit through which the reference signal passes at the time of the IQ calibration are connected to the same antenna.